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What is pneumonia?

Pneumonia is a type of chest infection. It affects the tiny air sacs in your lungs, called alveoli. When you have pneumonia, these air sacs get inflamed and fill with fluid. This makes it harder for you to breathe.

Diagram of the lungs, airways, bronchioles, and air sacs

More people get pneumonia in winter. This is because respiratory viral infections that spread easily from person to person, such as flu, are more common in the winter, and these increase your risk of developing pneumonia.

If you have a long-term lung condition, or care for someone who does, it’s a good idea to have a flu jab every year. Flu can be very serious, and cause complications such as pneumonia.

The flu vaccine is usually free for people at risk and is available from your GP and many high street chemists. It’s best to have your vaccine before the flu virus starts to circulate, which is usually mid-December.

Most people with pneumonia can be completely cured. But it can be life-threatening, and you should take it seriously even if you’re young and fit.

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What causes pneumonia?

Many kinds of bacteria and viruses can cause pneumonia.

The most common type of pneumonia is community-acquired pneumonia, which is when pneumonia affects somebody who is not already in hospital. The most common cause of community-acquired pneumonia is a bacterium called Streptococcus pneumoniae but there are many other causes. Community-acquired pneumonia is much less contagious than flu or a cold, because most people’s immune systems can kill the bacteria that causes it before they can cause an infection. Most people with community-acquired pneumonia are unlikely to give the disease to another person.  

As well as community-acquired pneumonia, other types include:

Hospital-acquired pneumonia: this is when pneumonia develops while you’re in hospital being treated for another condition or having an operation. People in intensive care on breathing machines are at most risk.

Viral pneumonia: common causes include the flu in adults and respiratory syncytial virus, particularly in children; this form of pneumonia is often contagious and can spread to affect others

Aspiration pneumonia: this is when pneumonia is caused by food going down the wrong way, or inhaling vomit, a foreign object or harmful substance. It’s fairly common in the elderly, or people who have conditions that cause swallowing difficulties or reduced level of consciousness

Fungal pneumonia: this is when pneumonia is caused by fungi. It’s rare in the UK and more likely to affect people with a weakened immune system

You might also hear the term ‘double pneumonia’. This means when you get pneumonia in both lungs. It’s a term used in America.

Can you catch pneumonia more than once?

Yes. Pneumonia is caused by many different microbes, and so getting it once does not protect you from getting it again. If you get pneumonia more than once you may need to have more investigations to understand why this has happened. It could be due to a problem in your chest or your immune system, and you may be referred to a specialist.

What are the symptoms of pneumonia?

If you have pneumonia, you’ll have symptoms that are similar to having flu or a chest infection. Symptoms may develop gradually over a few days but can progress much faster.

The main symptom is coughing. You may feel generally unwell, weak and tired, and you’ll probably have at least one of these symptoms too:

  • coughing up mucus that may become yellow or green
  • a high temperature – you might also sweat and shiver
  • difficulty breathing or getting out of breath quicker than normal
  • chest pain or discomfort
  • loss of appetite

Even if you have pneumonia, you may not have all these symptoms.

More severe cases may also cause:

  • quick breathing
  • confusion
  • low blood pressure
  • coughing up blood
  • rapid heartbeat
  • nausea and vomiting

Some people get a sharp pain in their chest when they breathe in and out. This may be because the thin lining between the lung and ribcage, called the pleura, is infected and inflamed. This inflammation, called pleurisy, stops your lungs moving smoothly as you breathe.

Diagram of the lungs and pleura (lining)

The symptoms of pneumonia are often very similar to those of other chest infections, such as bronchitis, COPD flare-ups or bronchiectasis flare-ups. To get a proper diagnosis you’ll need to visit your GP.

If you feel unwell with these symptoms, see your GP or call 111. If you have chest pain, a rapid heartbeat, quick breathing, shivers or confusion, get urgent advice from your GP or call 999. Take extra care if you’re over 65.

Who is most at risk of pneumonia?

You can get pneumonia at any age. Each year in the UK, about 5-11 adults out of every 1,000 get pneumonia.

Some groups of people are at higher risk from pneumonia. If you’re in one of these groups, you should take extra care to reduce your chances of catching pneumonia.

People in these at-risk groups include:

  • babies and young children
  • people over 65
  • people with long-term heart, lung, brain, liver or kidney diseases, or diabetes
  • people with cancer, especially those having chemotherapy
  • people who smoke or drink alcohol to excess
  • people on drugs that suppress the immune system, and those with HIV

People in hospital for other problems sometimes develop pneumonia while they’re there. This can be for several reasons including the use of mechanical ventilators, recent antibiotic use or because their resistance to infection has been weakened by other medical problems.

Next: how to prevent pneumonia >

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Last medically reviewed: October 2019. Due for review: October 2022

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.